1. Field of the Invention
The present invention relates generally to current-interrupting devices for electrical power distribution systems and more particularly to a rotating arc interrupter for a loadbreak switch which utilizes a main stationary contact that is positioned in the middle of an arc runner in the shape of a ring and a shunt contact that bridges the arc runner and that is above and coplanar with the main stationary contact.
2. Description of the Related Art
Various interrupting devices including rotating arc interrupters have been proposed that utilize magnetic fields to perform their functions.
For example, U.S. Pat. No. 4,032,736 is directed to a gas-pressurized electrical switch with a current-generated magnetic field for assisting arc extinction when the cylindrical movable and stationary contacts separate by relative longitudinal movement. An annular intermediate electrode is provided which is connected through a coil to the stationary contact bus. A central conductive pin is provided that is insulated from the other structure. Upon contact separation, arcing first occurs between the contacts and then commutating from the stationary contact to the annular intermediate electrode, with the arcing current flowing through the coil and the arc rotating. The arc then divides such that one part arcs between the movable contact and the central pin and the other part arcing between the central pin and the annular intermediate electrode, that part of the arc continuing to rotate. The arcing heats up the chamber to a positive pressure such that the gas flow extinguishes the arc.
The arrangement of U.S. Pat. No. 4,414,450 utilizes coaxial main contacts and commutation contacts along with compressed gas directed into an expansion chamber to perform an interrupting function. A stationary commutation contact 22 (reference numerals are that of the '450 patent) includes concentric portions, an annular part 221 in the configuration of a nozzle and a second part 222 in the shape of a hollow pin (head with tubular body) that is surrounded by a coil 3. The coil 3 is connected between the hollow pin 222 and the annular part 221. After separation of the main contacts, the current is commutated to the commutation contact 22 and the movable commutation contact 12 carried with the movable stationary contact. When the connection is broken between the commutation contacts, an arc is formed, with the arc being blown by the flow of quenching gas to commutate the arc from the annular portion 221 to the hollow pin portion 222, with current flow now occurring through the coil 3 to the annular portion 221. While the arc is rotated to a negligible extent, energy is pumped from the magnetic field into the random, turbulent gaseous motion of the arc column 5. This leads, in contrast to conventional transversely blown arcs, to the breaking of the arc and to a particularly effective mixing of the arc 5 with the surrounding cold gas. Another rotating arc arrangement with self-extinguishing expansion features is shown in U.S. Pat. No. 5,166,483.
U.S. Pat. No. 4,918,268 is directed to an arc-rotating magnetic-blast coil having a winding 23 with a conductive cup 1 and a conductive disk 21 that is electrically connected to a core of the winding 23. A moving conductive cup 2 and the conductive cup 1 form main contact areas, with arc-runner contact surfaces being provided by the conductive disk 21 of the stationary conductive cup 1 and a conductive disk of the movable conductive cup 2. These arc-runner disks are arranged to stay in contact after separation of the main contacts. When the arc runner disks separate, an arc is struck with current continuing to flow through the winding 23. The arc rotates to aid in current interruption.
The arrangements in U.S. Pat. Nos. 4,301,340 and 4,301,341 operate in an insulating gas environment and include main contacts and an arcing electrode to which an arc is transferred after the opening of the main contacts. The arcing current passes through a field coil to create an arc-rotating magnetic field to extinguish the arc. The structure includes a pivoting main contact which is pivoted into the tubular arcing electrode surrounded by the field coil.
In U.S. Pat. No. 5,003,138, a rotating-arc circuit is provided in parallel with the main contacts. A stationary cylindrical electrode is disposed inside a coil and cooperates with a movable arcing contact which moves over a path from one point in contact with the inner periphery of the cylindrical electrode to a point central of the cylindrical electrode.
While the prior art arrangements may be useful to provide current interrupting devices for general purposes and for use in circuit breakers, these arrangements are relatively large and cumbersome and do not lend themselves for use in distribution switchgear where small size and the visibility of an open switch gap is desirable.